Sunday, December 11, 2022

Nature: Another Toilet Plume Study To Consider


Over the past decade we've looked repeatedly at case studies and laboratory experiments that suggest that the flushing of toilets may create an aerosolized `toilet plume'; one which can potentially spread viruses or bacteria through the air.   

Pathogens that could theoretically stay `aloft' for 20 or 30 minutes, or coat nearby surfaces, and remain viable for hours.  

In 2012, in Norovirus: The Gift That Keeps On Giving, we looked at an outbreak of norovirus that was believed due to just such an event, when a reusable open top grocery bag stored in a hotel bathroom became contaminated by one infected individual, and ended up spreading the virus to the other members of a girls soccer team.

The incident was described in the Journal of Infectious Diseases (see A Point-Source Norovirus Outbreak Caused by Exposure to Fomites by Kimberly K. Repp, and William E. Keene), where the authors wrote:
Aerosolization of vomit and feces has been demonstrated to be of major importance in norovirus outbreaks [13]. Even viruses aerosolized from flushing a toilet can contaminate surfaces throughout a bathroom [14]. Once a fomes is contaminated, transfer to hands and other animate objects can readily occur [15]. The more confined the space (eg, most bathrooms), the more intense would be the “fallout” [13].
Also in 2012, the Journal of Hospital Infection published Potential for aerosolization of Clostridium difficile after flushing toilets: the role of toilet lids in reducing environmental contamination risk, which found:
C. difficile was recoverable from air sampled at heights up to 25 cm above the toilet seat. The highest numbers of C. difficile were recovered from air sampled immediately following flushing, and then declined 8-fold after 60 min and a further 3-fold after 90 min. Surface contamination with C. difficile occurred within 90 min after flushing, demonstrating that relatively large droplets are released which then contaminate the immediate environment. The mean numbers of droplets emitted upon flushing by the lidless toilets in clinical areas were 15-47, depending on design. C. difficile aerosolization and surrounding environmental contamination occur when a lidless toilet is flushed.

Lidless conventional toilets increase the risk of C. difficile environmental contamination, and we suggest that their use is discouraged, particularly in settings where CDI is common.

In 2015, with NIOSH Video: Adventures In Toilet Plume Research, researchers at NIOSH and the University of Oklahoma completed a build (see photo below) that allowed them to test the amount of aerosols generated at different flush rates.

Their research showed that high powered flushing units – such as those commonly used in hospital settings – gave off more aerosols than standard toilets.  Something for nursing staff to think about the next time they are charged with emptying an emesis basin or bedpan from a suspected norovirus patient.
Three years later, in 2018 (see Toilet Bowl Sunday) we looked at two related studies:

Bioaerosol concentrations generated from toilet flushing in a hospital-based patient care setting

Health risks from exposure to Legionella in reclaimed water aerosols: Toilet flushing, spray irrigation, and cooling towers

And again in 2020 (see EID Journal: More Toilet Plume Research In A Time Of COVID-19), when we looked at an EID Journal dispatch (see Transmission of Legionnaires’ Disease through Toilet Flushingalong with a study that suggested  closing the lid may reduce, but not eliminate, the aerosols generated by a flush toilet.

This week the journal Nature published a new report on the aerosolization potential of commercial toilets (see below), which - considering out current energetic winter viral epidemic - is well worth noting. 

I've posted the link and abstract below, along with excerpts from a recent article in The Conversation by one of the authors of this study. 

Commercial toilets emit energetic and rapidly spreading aerosol plumes

Scientific Reports volume 12, Article number: 20493 (2022) 


Aerosols can transmit infectious diseases including SARS-CoV-2, influenza and norovirus. Flushed toilets emit aerosols that spread pathogens contained in feces, but little is known about the spatiotemporal evolution of these plumes or the velocity fields that transport them. Using laser light to illuminate ejected aerosols we quantify the kinematics of plumes emanating from a commercial flushometer-type toilet, and use the motion of aerosol particles to compute velocity fields of the associated flow. The toilet flush produces a strong chaotic jet with velocities exceeding 2 m/s; this jet transports aerosols to heights reaching 1.5 m within 8 seconds of initiating a flush. Quantifying toilet plumes and associated flow velocities provides a foundation for future design strategies to mitigate plume formation or to disinfect pathogens within it.


From The Conversation.

Toilets spew invisible aerosol plumes with every flush – here’s the proof, captured by high-powered lasers
Published: December 8, 2022 5.18am EST

Every time you flush a toilet, it releases plumes of tiny water droplets into the air around you. These droplets, called aerosol plumes, can spread pathogens from human waste and expose people in public restrooms to contagious diseases.

Scientific understanding of the spread of aerosol plumes – and public awareness of their existence – has been hampered by the fact that they are normally invisible. My colleagues Aaron True, Karl Linden, Mark Hernandez, Lars Larson and Anna Pauls and I were able to use high-power lasers to illuminate these plumes, enabling us to image and measure the location and motion of spreading aerosol plumes from flushing commercial toilets in vivid detail.


Limiting toilet plume spread

Our experimental methodology provides a foundation for future work to test a range of strategies to minimize the risk of exposure to diseases from flushing toilets. This could include assessing changes to aerosol plumes emanating from new toilet bowl designs or flush valves that change the duration or intensity of the flush cycle.

Meanwhile, there are ways to reduce human exposure to toilet plumes. An obvious strategy is to close the lid prior to flushing. However, this does not completely eliminate aerosol plumes, and many toilets in public, commercial and health care settings do not have lids. Ventilation or UV disinfection systems could also mitigate exposure to aerosol plumes in the bathroom.

          (Continue . . . )

Until relatively recently the importance of aerosol transmission of viruses and bacteria has been downplayed, with many citing an `effective range' of less than two meters, a very brief `suspension time', and short-term viability in the environment as limiting factors. 

Today, with studies like EID Journal: Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021, we can see that viruses are far more capable of spreading over long distances than previously believed. 

How often people are infected due to toilet plumes is unknown, but it does appear to be a likely route of infection.  Knowing what I know now, I plan on keeping a face mask handy anytime I might be forced to use public restroom.

Even after our current pandemic has ended.